Transposed rotor winding



Aug. 2, 1955 J. F. HEIDBREDER 2,714,675

TRANSPOSED ROTOR WINDING Filed March 30, 1954 Fig.|.

151 I64 155, lllllllllllm.

Fig.2.

rates Patent ()fific 2,714,675 Patented Aug. 2, 1955 2,714,675 TnANsPosED ROTOR WINDING John F. Heidbreder, Irwin, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 30, 1954, Serial No. 419,808 4 Claims. (Cl. 310-213) My invention relates to wound-rotor induction-motors or other alternating-current dynamo-electric machines, which are operable at such high speeds as to require banding around the end-winding portions of the rotor-winding for restraining the same against centrifugal force, and which are of such size and rotor-winding frequency as to require a stranded-conductor rotor-winding, with some kind of transposition of the strands of the coil-sides, in order to reduce the heating which would otherwise result from the stray-load loss or eddy-current loss due to the slot leakage flux.

Heretofore, the Roebel transposition has commonly been applied to the stator windings of large turbine generators where there has been no centrifugal force on the end windings. Heretofore, also, large wound-rotor induction-motors have been built with unstranded rotor windings or secondary windings, which were satisfactory because of the low frequency of the currents which were induced in said windings. Such stranded or unstranded rotor-windings were made from heavy copper strap, having straight coil-side portions which were held in the rotor-slots by wedges, and having extending portions which were bent down as they left the rotor-core, so as to provide radial space for the banding which was required to support the coil-ends or end-winding portions. These bent-down portions were necessary, because otherwise it would have been necessary to provide excessively deep rotor-slots, which would seriously impair the power factor and the pull-out torque of the induction-motor.

My invention relates particularly to a type of large wound-rotor induction-motor which is adapted to be operated, at times, at a speed which is considerably lower than the synchronous speed. As the speed of the motor is reduced, the frequency of the rotor-current increases, and the eddy-current loss becomes excessive, resulting in excessive rotor-winding heating. In order to reduce this loss, the rotor coils are made up of small copper strands, which must be suitably transposed. The natural thought would be to make such a stranded rotor-coil with the usual Roebel interposition which extends throughout the coil side portions which lie in the rotor-slots, and to make such a rotor-winding with the coil-extensions bent down as they left the rotor-core, so as to provide a reduced-diameter end-winding portion, above which there would be sufficient radial room for the banding which would be necessary to take care of the high-speed operation of the motor. Such a stranded rotor-coil, however, would not, in most cases, have sufiicient stiifness or strength to support itself between the rotor-core and the point where there is suflicient space to start the banding. Therefore, the coil must leave the rotor-core at a point which is a sufiicient radial distance below the rotor-periphery to provide space for the band. This, in turn, would cause the stranded coil-side portions, which lie in the rotor-slots, to be so far below the rotor-surface or periphery, as to result in a prohibitively low power factor and a prohibitively low pull-out torque.

My invention provides for a special construction whereby the end-winding banding can come close to the ends of the rotor-core without serious impairment of the power factor or the pull-out torque of the motor, and whereby the rotor-winding may be stranded in order to reduce the stray-flux load-loss.

In the drawing, an exemplary form of embodiment is shown, in which my invention is applied to a large woundrotor induction-motor in which the rotor-core has winding-receiving slots, and in which,

Figure l is a developed plan view of a portion of the rotor-core, with one top coil-half and one bottom coilhalf in place, the two coil-halves being joined together to constitute one coil, and

Fig. 2 is a fragmentary longitudinal sectional view of the completed rotor-member, with a fragmentary sectional View of a corner of the stator member, the sectionplane being indicated by the line 11-11 in Fig. 1.

In Fig. 2, I have indicated an induction-motor having a stator 151 and a rotor 152. The rotor includes a rotorcore 153 which is illustrated as having 150 winding-receiving slots, which are numbered from 1 to 150, although it will be understood that this number is only illustrative. The rotor carries a secondary winding which is made up of 150 top coil-halves 155, and 150 bottom coil-halves 156, each coil-half having a coil-side portion 157 which lies in one of the slots, and two end-winding portions 158 and 159, which extend beyond the respective ends of the rotor-core 153. The coil-sides 157 are retained in the rotor-slots by means of slot-wedges 161 (Fig. 2). The top and bottom end-winding portions of the coilhalves and 156 are restrained against centrifugal force by means of banding 162 (Fig. 2). Since however, the illustrated machine has a very high peripheral rotor-velocity, a separate bottom-layer banding 163 is applied to the end-winding portions of the bottom coilwinding portions of the coil-halves 155' and 156, which is filled with an insulating padding or wrapping 164, laid over the bottorn-layer banding 163.

The bottom-layer end-winding portions of the coilhalves 156 are laid over a suitable cylindrical coil-support 165, in accordance with the usual practice. After and bottom layers of the winding have coil-halves are joined together by suitable strap-connectors 166, which are silver-soldered in place in accordance with a familiar construction.

In accordance with my invention, each of the rotor-slots 1 to 150, for all of its length except close to its ends, has radial depth which is sufiicient only for its coil-sides 155 and 156, its wedge 161, and any necessary insulation the end-winding banding 162, or for the two bands 162 and 163, if both bands are used. Each of the top and bottom coil-sides 155 and 156 is also bent down, at the places a and b where the slots become deeper, as shown in Fig. 2.

The coil-halves 155 and 156 of the rotor-winding are made of a stranded construction, with two strands in the width of each slot, as in the standard Roebel transposition. In the illustrated motor, as actually constructed, there are twenty-four strands, arranged in two stacks of twelve, but for clarity of illustration, I have shown only five strands in each stack. The two stacks of strands are commonly wrapped around with a light Wrapping of insulation, which I have assumed to be transparent, so that the strands are visible in the drawing. The conductor-strands are commonly untransposed in the end-winding portions 158 and 159, because the leakage-flux in this region is low enough to remove the need for transposition, and also to facilitate the necessary bending of these end-winding portions. Also, the pattern of the leakage-flux at the end-windings is so complicated and so varying that transposing the strands there would only partially reduce any eddy-current loss in this region.

In my present invention, the strands in the vicinity ,of each of the bent-down portions of the coil-sides 157 are also left untransposed, so as to avoid the difliculty of bending a transposed portion without damage to the insulation. In accordance with my invention, at least when it is necessary to reduce the eddy-current loss to a minimum, the conductor-strands are also left untransposed at the centers of the coil-sides, between the points and d, for a reason which will shortly be explained. The conductor-strands are transposed by one-half of a complete transposition at each of the two other portions of each coil-side 157, that is, between the points e and c, and between the points d and f, the point c being close to the bent-down portion a while the point 1 is close to the similar bent-down portion at the other end of the coil-side.

The effect of the half-transposition of the strands in the portion from e to c is to bring the top strand of each coilside down to the bottom, or to cause each of the other strands to make half of its transposition around the conductor, starting from whatever position it starts from, in passing between said two points. Similarly, the effect of the half-transposition between the points d and f is to bring the bottom strand back up to the top, in passing between these two points in any one of the 300 coil-halves. There will be differential voltages, which are induced between the strands, because of slot-leakage flux, in each of the untransposed slot-lying portions at each end of each coil-side. My untransposed central portions, c to d, in each coil-side, are for the purpose of neutralizing, as well as possible, these differential voltages which are induced in the untransposed end-portions of each coilside, the voltage-neutralization varying from partial to complete, between the various strands, depending on their positions. In general, the total axial length of the untransposed central portion 0 to d is greater than the combined lengths of the two unstranded ends of that coil-side, for a minimum stray-load loss.

It will be noted that my increased slot-depth slotends, at b, results in two things. It brings down the diameter of the end-winding portions to a value which leaves radial room for the banding, and it leaves the major portion of each slot, from the point a near one end to the corresponding point near the other end, with a minimum possible radial depth, so as to bring the major portions of the coil-sides as close as possible to the rotorperiphery, so as to avoid an impairment of the power factor and the pull-out torque of the motor The fact that the end-winding portions, as they emerge from the respective ends of the rotor-core, are at the same reduced diameter as the rest of the end-winding portions, makes it possible to apply the bandings 162 and 163 up to a point close .to the rotor-core 153, leaving no portion of the mechanically weak strands of the end windings unprotected against centrifugal force.

At the bent-down end-portions of each of the coilsides, the region from a to b, and from there on out to the nearby end of the core, the strands are protected against centrifugal force by means of suitably shaped fillers 171 and 172, which fill in the spaces and transmit the centrifugal force to the slot-closing wedges 161.

My special slot-shape is also useful in rotor-members having such low frequencies as to require no stranding of the rotor-winding conductors.

While I have illustrated my invention in only a single exemplary form of embodiment, I wish it to be understood that various changes, and substitutions, and omissions may be made within the scope, of the invention.

I claim as my invention:

1. A wound-rotor induction-motor having a stator and a rotor, said rotor having a rotor-core having winding-receiving slots, said rotor also having a secondary winding having coil-side portions lying in said slots, and having end-winding portions extending beyond said rotorcore, said rotor still further having slot-wedges for retaining the coil-sides in said slots, and having banding around the end-winding portions for restraining the same against centrifugal force, characterized by each slot, for all of its length except close to its ends, having a radial depth which is suflicient only for its coil-sides, its wedge, and the necessary insulation, each slot becoming deeper at each end to provide radial room for the end-winding banding to come close to the end of the rotor-core, each coil-side being bent down at the places where said slots become deeper, and said rotor having shaped fillers over the downwardly bent ends of the respective coil-sides to restrain said ends against centrifugal force.

2. An alternating-current dynamo-electric machine having a stator and a rotor, said rotor having a rotorcore having winding-receiving slots, said rotor also having a stranded-conductor rotor-winding having coil-side portions lying in said slots, and having end-winding portions extending beyond said rotor-core, said rotor still further having slot-wedges for retaining the coil-sides in said slots, and having banding around the end-winding portions for restraining the same against centrifugal force, characterized by each slot, for all of its length except close to its ends, having a radial depth which is suflicient only for its coil-sides, its wedge, and the necessary insulation, each slot becoming deeper at each end to provide radial room for the end-winding banding to come close to the end of the rotor-core, each coil-side being bent down at the places where said slots become deeper, the conductor-strands beinguntransposed in the end-winding portions, and at the ends of the coil-sides in the vicinity of the places where the coil-sides are bent down, the conductor-strands being transposed at some other place or places in each coil-side, and said rotor having shaped fillers over the downwardly bent ends of the respectivecoil-sides to restrain said ends against centrifugal force.

3. An alternating-current dynamo-electric machine having a stator and a rotor, said rotor having a rotorcore having winding-receiving slots, said rotor also having a stranded-conductor rotor-winding having coil-side portions lying in said slots, and having end-winding portions extending beyond said rotor-core, said rotor still further having slot-wedges for retaining the coil-sides in said slots, and having banding around the end-winding portions for restraining the same against centrifugal force, characterized by each slot, for all of its length except close to its ends, having a radial depth which is sulficient only for its coil-sides, its wedge, and the necessary insulation, each slot becoming deeper at each end to provide radial room for the end-winding banding to come close to the end of the rotor-core, each coil-side being bent down at the places where said slots become deeper, the conductorstrands being untransposed in the end-winding portions, and at the ends of the coil-sides in the vicinity of the places where the coil-sides are bent down, and also at the centers of the coil-sides, the conductor-strands being transposed by one-half of a complete transposition at each of the other portions of each coil-side, the length of the central untransposed portion of each coil-side being such as'to suitably neutralize the differential voltages induced between strands by the slot-leakage flux in the untransposed portions at the ends of the coil-sides, and said rotor having shaped fillers over the downwardly bent ends of the respective coil-sides to restrain said ends against centrifugal force.

1 4. A wound-rotor inductor-motor having a stator and a rotor, said rotor having a rotor-core having windingreceiving slots, said rotor also having a stranded-conductor secondary winding having coil-side portions lying the rotor-core, each coil-side being bent down at the places Where said slots become deeper, the conductorstrands being untransposed in the end-winding portions,

come close to the end of 10 and at the ends of the coil-sides in the vicinity of the places Where the coil-sides are bent down, and also at the centers of the coil-sides, the conductor-strands being transposed by one-half of a complete transposition at each of the other portions of each coil-side, the length of the central untransposed portion of each coil-side unstranded ends of that coil-side, and said rotor having shaped fillers over the downwardly bent ends of the respective coil-sides to restrain said ends against centrifugal force.

No references cited. 

